Conveying system having endless drive medium and conveying method

1. A transport system comprising: an endless driving medium configured to rotate in a circulating manner; a plurality of carriers attached to the endless driving medium and configured to hold articles for transportation; a plurality of stations provided along the endless driving medium; and a moving distance sensor configured to measure a moving distance of the endless driving medium; wherein each of the plurality of stations includes: a hand configured to load articles to and unload articles from the carriers; a driver configured to move the hand both in a rotation direction of the endless driving medium and in a vertical direction; a first carrier sensor configured to detect the carriers at a predetermined position upstream of the hand along the rotation direction of the endless driving medium; a second carrier sensor configured to detect the carriers at a position downstream of the first carrier sensor; and a signal processor configured to make the driver drive the hand based on the moving distance measured by the moving distance sensor, from detection of the carriers by the first carrier sensor; wherein the signal processor evaluates a difference between the moving distance measured by the moving distance sensor from detection of the carriers by the first carrier sensor and a distance between the first carrier sensor and the second carrier sensor at the second carrier sensor detecting the carriers, and if the difference is greater than an allowable value, the signal processor stops movement of the hand by the driver.

2. The transport system according to claim 1 , wherein the first carrier sensor detects the carriers at a predetermined position downstream of a position of starting movement of the hand, and the hand is driven after detection of the carriers by the first carrier sensor and before detection of the carriers by the second carrier sensor.

3. The transport system according to claim 2 , further comprising a second moving distance sensor configured to measure a moving distance from a position of starting movement of the hand; at the second carrier sensor detecting the carriers, the signal processor evaluates a difference between the moving distance measured by the second moving distance sensor and a predetermined moving distance, and with the difference greater an allowable value, the signal processor makes the driver stop the hand.

4. The transport system according to claim 3 , wherein the driver drives the hand to pass the second carrier sensor at a same time and at a same velocity with the carrier.

5. A transport method comprising the steps of: attaching a plurality of carriers to hold articles to an endless driving medium configured to rotate in a circulating manner, providing a plurality of stations along the endless driving medium; measuring a moving distance of the endless driving medium; providing a hand being configured to load articles and to unload articles from the carriers for each of the plurality of stations; detecting the carriers by a first carrier sensor at a predetermined position upstream of the hand along a rotation direction of the endless driving medium; detecting the carriers by a second carrier sensor at a position downstream of the first carrier sensor; driving the hand by the driver based on the moving distance of the endless driving medium, from detection of the carriers by the first carrier sensor; and evaluating a difference between the moving distance of the endless driving medium from detection of the carriers by the first carrier sensor and a distance between the first carrier sensor and the second carrier sensor at the second carrier sensor detecting the carrier, and if the difference is greater than an allowable value, stopping movement of the hand by the driver.